GaAs and InP optoelectronic devices, including vertical cavity surface-emitting lasers (VCSELs) and high performance diodes, often use a more electrically conducting “aperture” in a nonconducting layer to direct electrical current into a central light-emitting region or “active” region. In most of these GaAs and InP systems, aperture materials are also selected to have a higher refractive index than the nonconducting layer material, thereby enabling the aperture to also confine the generated optical fields. See U.S. Pat. No. 7,160,749 entitled “Method and Structure for Eliminating Polarization Instability in Laterally Oxidized VCSELs” by Chua et al. which is hereby incorporated by reference in its entirety. In some “anti-resonant” structures, the refractive index of the aperture is designed to have a lower value than surrounding areas to controllably induce losses to higher order modes.
Various methods are available for forming the conducting aperture. In one method, a chemical etch to form a pattern followed by a regrowth of the aperture material in the patterned layer openings is used to form the aperture. Such a procedure is described in D. Zhou and L. J. Mawst, Appl. Phys. Lett., v.76 (13), 2000, pp. 1659-1661 which is hereby incorporated by reference. Alternate methods of forming a conducting aperture in an AlGaAs layer include converting select non-aperture regions of the AlGaAs layer into an insulating oxide through selective wet thermal oxidation. The oxidized material also has a lower refractive index than the unoxidized material.
Although conducting apertures and/or light guiding apertures would benefit an indium aluminum gallium nitride (InAlGaN) light emitting device, a suitable means for forming such apertures has not been available. Chemical etching of nitride heterostructures followed by subsequent regrowth in patterned layer openings has proved difficult because InAlGaN crystalline alloys are very stable and are therefore resistant to chemical attack. Oxidation techniques have also been difficult to implement because nitride based materials are not easily oxidized.
Thus a method of forming apertures that channel current and/or confine optically generated fields in a nitride based light emitting structure is needed.